Determinants of Lipid Domain Size

Lipid domains less than 200 nm in size may form a scaffold, enabling the concerted function of plasma membrane proteins. The size-regulating mechanism is under debate. We tested the hypotheses that large values of spontaneous monolayer curvature are incompatible with micrometer-sized domains. Here, we used the transition of photoswitchable lipids from their cylindrical conformation to a conical conformation to increase the negative curvature of a bilayer-forming lipid mixture. In contrast to the hypothesis, pre-existing micrometer-sized domains did not dissipate in our planar bilayers, as indicated by fluorescence images and domain mobility measurements. Elasticity theory supports the observation by predicting the zero free energy gain for splitting large domains into smaller ones. It also indicates an alternative size-determining mechanism: The cone-shaped photolipids reduce the line tension associated with lipid deformations at the phase boundary and thus slow down the kinetics of domain fusion. The competing influence of two approaching domains on the deformation of the intervening lipids is responsible for the kinetic fusion trap. Our experiments indicate that the resulting local energy barrier may restrict the domain size in a dynamic system.     

OXIDATIVE DEHYDROGENATION OF ETHANE OVER A MONOLITH COATED BY MOLYBDENUM-VANADIUM-NIOBIUM MIXED-OXIDE CATALYST

Oxidative dehydrogenation of ethane to ethylene was investigated using Mo 0.71 V 0.21 Nb 0.08 mixed-oxide catalyst, in powder form and coated over a monolith. At 570°C and with a feed stream containing an O 2 /C 2 H 6 mole ratio of one, ethylene selectivity value reaching to 96% was obtained at a conversion level of about 5% with the monolith-supported catalyst. DRIFTS studies indicated the presence of adsorbed ethoxide species. The proposed reaction scheme for the production of ethylene includes the elimination of β-hydrogen of adsorbed species by the lattice oxygen.     

A method for local deconvolution

A new method for deconvolution of one-dimensional and multidimensional data is suggested. The proposed algorithm is local in the sense that the deconvolved data at a given point depend only on the value of the experimental data and their derivatives at the same point. In a regularized version of the algorithm the deconvolution is constructed iteratively with the help of an approximate deconvolution operator that requires only the low-order derivatives of the data and low-order integral moments of the point-spread function. This algorithm is expected to be particularly useful in applications in which only partial knowledge of the point-spread function is available. We tested and compared the proposed method with some of the popular deconvolution algorithms using simulated data with various levels of noise.     

The behavior of organic components in copper recovery from electroless plating bath effluents using 3D electrode systems

An electrochemical method was applied for the recovery of copper both from the spent solutions and from the rinse waters of electroless copper plating baths, containing copper sulfate, formaldehyde, quadrol, and NaOH. Experiments were conducted in a rotating packed cell (Rollschichtzelle) to investigate the effects of current density, electrolyte composition, temperature, and pH on the copper recovery. All the copper (final CCu=0.1 ppm) was recovered from the waste and rinse waters of chemical copper plating plants with 70% current efficiency by the electrochemical treatment in a rotating packed cell at 130 A/m2 current density, room temperature, with 5mm diameter cathode granules, with the presence of formaldehyde, and with a specific energy consumption of 3.2-3.5 kW h/kg Cu. On the other hand, final copper concentrations of 5 ppm were reached with 62% current efficiency and 5.5-5.8 kW h/kg Cu specific energy consumption, with electrolytes containing no formaldehyde.     

Assessment of metabolic activity of human cells in solution and in polymer matrix with the use of metabolite-sensitive sensors

We developed metabolite-sensitive electrochemical sensors on the basis of electrodes modified with a thick film of carbon nanotubes. Modified electrodes provide efficient pre-adsorption of cellular metabolites and their sensitive detection using anodic square-wave voltammetry. On the electrode surface both adhered and non-adhered human cells produce three oxidation peaks at the potentials of + 0.82, + 1.05, and + 1.17 V attributed to three groups of cellular metabolites: amino acid-derived antioxidants including glutathione, guanine nucleotides, and also adenine nucleotides including ATP. The electrochemical response was well correlated with cell viability, intracellular ATP level and induction of apoptosis, as determined by independent assays. Developed sensors allow for robust and cost-effective assessment of ATP in cells in contrast to enzyme-based electrodes and conventional bioluminescent assay. Results can be used for rapid analysis of human cells for the purpose of medical diagnostics, transplantology, and toxicological screening. Additionally, we combined modified electrodes with human cells entrapped in agarose matrix. The resulting biosensor allowed for electrochemical monitoring of metabolic activity and death of cells within polymeric matrix that is of interest for tissue engineering applications.     

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

The possibility of triggering correlated phenomena by placing a singularity of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer graphene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back-gated device architecture for angle-resolved photoemission measurements with a nano-focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these features is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.     

Suitability of Au- and self-assisted GaAs nanowires for optoelectronic applications

The incorporation of Au during vapor-liquid-solid nanowire growth might inherently limit the performance of nanowire-based devices. Here, we assess the material quality of Au-assisted and Au-free grown GaAs/(Al,Ga)As core-shell nanowires using photoluminescence spectroscopy. We show that at room temperature, the internal quantum efficiency is systematically much lower for the Au-assisted nanowires than for the Au-free ones. In contrast, the optoelectronic material quality of the latter is comparable to that of state-of-the-art planar double heterostructures.